Marsilio Ficino’s Platonic Theology, Volume II

23In the same way, you will deny that light exists in the sphere of fire because it is not discerned by the eyes. But the sun's own radiance would exist even if it were not seen, since it exists now and is not seen by owls. What we see is a certain splendor of it mixed with vapors rather than the radiance itself; yet from this splendor we infer that the radiance itself exists somewhere. So too, from the light of the stars, which is its image, we infer that spiritual light inheres in celestial souls. Do you not know that the activity of light is nothing other than to shine, and that it glows more clearly the farther it is separated from dense bodies? Separate it from all matter: it will shine more wonderfully, and then it will live most of all, if it is ever to live. For where activity increases, life also increases, especially since all these things live through its heat. It will also sense, so to speak, since through its rays all these things sense; yet it will not itself be sensed. By its subtlety it will elude the sharpness of the eyes, and by the abundance of its intelligible radiance it will surpass the capacity of earthly sight.

24You know that among the elemental spheres the lowest fire descends so far toward the nature of the highest air, while the highest air in turn rises so far toward that fire, that the fire appears to be scarcely anything other than subtle air, and the air a denser fire. Thus anyone who sees that air can affirm without falsehood that he has seen fire. The same comparison holds between the lowest mind, such as the rational soul, and the sublime body which is heaven. The soul is therefore in a certain way a subtle heaven, and heaven a denser soul. Whoever looks up at heaven looks forth upon the soul.